rdcs

From DavinciWiki

Contents: Description, Arguments, Usage, Examples, Images, Sub-Functions, Related Functions, Source

Description

Perform a running decorrelation stretch on one or three bands of the data.

rdcs() performs an individual decorrelation stretch on every sub-section of the array defined by an x and y dimension. It then uses an overlap of half of the defined size to blend it with the next section of the data. This is done so there is no visible seam and the stretch is essentially "running" or changing over the whole data set. This process helps eliminate image wide variations and maximizes local variation producing a "harder" stretch. This is evident when looking at the sample images below.

Changing the x and y sizes will ultimately determine how local or regional features affect the stretch.

Uses dcs as the stretching function.

Arguments and Return Values

Arguments: Accepts any 3 or 1 band numeric array

Return Value: A stretched byte array

Usage

Syntax: rdcs(data=VAR [, ignore=FLOAT] [, ysize=INT] [, xsize=INT] [, variance=FLOAT] [, sample=VAR] [, verbose=1])

'data' - Any numeric array

'ignore' - Ignore value of the black space. Default of -32768.

'ysize' - An integer designating the size of the data subsets in the y direction. Default of 1000.

'xsize' - An integer designating the size of the data subsets in the x direction. Default of 4000.

'variance' - Variance of the stretch. Default of 50.

'sample' - Apply the stretch of the sample numeric array to the original data

'verbose' - Print the segment of the image that is being manipulated. Default is 0.

NOTE: This function returns a value of 1 as the minimum data value and 0 for black space as of version 1.02

Examples

dv> a
342x3664x10 array of float, bsq format [50,123,520 bytes]

The two methods below are equivalent and yield the same results, but the second can be used for more memory efficient processing.

dv> b = rdcs(cat(a[,,8],a[,,7],a[,,5],axis=z),ysize=500,xsize=1000,ignore=-32768)
342x3664x3 array of byte, bip format [3,759,264 bytes]

dv> b = rdcs(data=cat(a[,,8],a[,,7],a[,,5],axis=z),ysize=500,xsize=1000,ignore-=32768)
342x3664x3 array of byte, bip format [3,759,264 bytes]

Images

The stretch of the left image is dominated by the canyon's huge difference in values (visible as orange in the bottom of the canyon) and consequently the plains appear washed out by the purple/blue color. The stretch on the right is more consistent throughout, normalizing the plains above the canyon to have a similar stretch as the canyon itself.